Introduction
In English criminal law, the principle of causation is fundamental to establishing liability for all result crimes. For a defendant to be found guilty of a crime such as murder, manslaughter, or causing grievous bodily harm, the prosecution must prove beyond reasonable doubt that their actions caused the prohibited consequence. This link between the defendant's conduct and the final result is known as the chain of causation. The law has developed a two-stage test, requiring both factual and legal causation to be established. However, the seemingly simple chain of causation can be complicated by subsequent events, known as a novus actus interveniens (a new intervening act), which may be sufficient to break the chain and absolve the defendant of liability. This essay will explore the principles of factual and legal causation before examining the key circumstances in which the chain of causation may be broken. It will be argued that while the core principles provide a structured framework, their application, particularly in cases involving medical intervention and the victim’s own actions, relies heavily on judicial policy and common sense, which can sometimes lead to results that appear inconsistent or harsh.
The Two-Stage Test: Factual and Legal Causation
The first stage of the causation inquiry is to establish factual causation. This is determined by the ‘but for’ test: but for the defendant’s conduct, would the result have occurred? If the answer is no, then the defendant is the factual cause of the result. The leading authority for this principle is R v White [1910] 2 KB 124. In this case, the defendant put cyanide in his mother's drink with the intention of killing her. However, she died of a heart attack before the poison could take effect. Applying the ‘but for’ test, the court found that she would have died regardless of his actions. Therefore, he was not the factual cause of her death and could not be convicted of murder, although he was convicted of the separate crime of attempted murder. The ‘but for’ test acts as a preliminary filter, excluding cases where the defendant’s act had no causal connection to the outcome.
If factual causation is established, the prosecution must then prove legal causation. This is a more complex, normative inquiry designed to determine whether it is fair to attribute the result to the defendant. The law does not require the defendant’s act to be the sole or even the main cause of the result, but it must be an ‘operating and substantial’ cause (Herring, 2022). The requirement that the cause be ‘substantial’ means that it must be more than minimal; it cannot be a ‘slight or trifling link’, as stated in R v Kimsey [1996] Crim LR 35. The requirement that the cause be ‘operating’ means that it must still be active at the time the result occurs.
The case of R v Smith [1959] 2 QB 35 provides a powerful illustration. A soldier was stabbed by the defendant during a barrack-room fight. On the way to the medical station, he was dropped twice. At the station, he received treatment which was later described as "thoroughly bad" and likely affected his chances of recovery. Despite this, the court held that the stab wound was still an "operating and substantial cause" of his death. The defendant’s conviction for murder was upheld. Lord Parker CJ famously stated that "if at the time of death the original wound is still an operating and substantial cause, then the death can properly be said to be the result of the wound, albeit that some other cause of death is also operating." This establishes a high threshold for breaking the chain of causation; as long as the initial injury remains a significant cause, later contributory factors will not absolve the defendant.
Breaking the Chain of Causation: Novus Actus Interveniens
Even where factual and legal causation are initially present, the chain of causation may be broken by a novus actus interveniens. This is a new, intervening act which is so significant that it renders the defendant’s original act no longer an operating and substantial cause of the result. Such acts can be categorised into three main types: acts of a third party, acts of the victim, or medical intervention.
A key principle is that a "free, deliberate and informed" act of a third party will generally break the chain of causation (R v Pagett (1983) 76 Cr App R 279). In Pagett, the defendant, armed and resisting arrest, used his pregnant girlfriend as a human shield while he shot at police officers. The police returned fire, killing the girlfriend. The defendant argued that the police officers' actions broke the chain of causation. The Court of Appeal disagreed, holding that the police officers’ actions were not free and voluntary. Instead, they were a foreseeable and justified response, performed in the execution of their legal duty and in self-preservation. Therefore, the defendant’s conduct in creating that dangerous situation remained a substantial cause of the death.
The position regarding medical intervention is less straightforward. The courts have shown a significant reluctance to allow medical negligence to break the chain of causation. The classic authority is R v Cheshire [1991] 1 WLR 844. The defendant shot the victim, who then required a tracheotomy in hospital. The victim’s initial wounds were healing, but he died from complications arising from the tracheotomy, which the doctors failed to recognise. The defendant argued that this negligent treatment broke the chain. The Court of Appeal rejected this, holding that medical negligence would only break the chain of causation if it was "so independent of the defendant's acts, and in itself so potent in causing death, that they regard the contribution made by his acts as insignificant." This sets an extremely high bar. The decision in Cheshire is often contrasted with the much older case of R v Jordan (1956) 40 Cr App R 152, where the victim was stabbed and, while his wound was largely healed, was given an antibiotic to which he was known to be allergic. This was deemed "palpably wrong" treatment and was held to have broken the chain. Academics and courts have since sought to limit Jordan to its own highly exceptional facts (Simester and Sullivan, 2019), with Cheshire representing the modern approach, which heavily favours holding the original wrongdoer responsible for the consequences.
The Victim's Contribution
The victim’s own actions can also be considered as a potential intervening act. This arises in two main contexts: the ‘fright and flight’ cases and the ‘thin skull’ rule. In ‘fright and flight’ cases, the question is whether the victim’s reaction to the defendant’s threat was foreseeable. In R v Roberts (1971) 56 Cr App R 95, a young woman jumped out of a moving car to escape the defendant’s unwanted sexual advances and was injured. The court held that her actions did not break the chain of causation, as they were a reasonably foreseeable consequence of what the defendant was doing. The test was whether the victim’s reaction was "so daft… or so unexpected… that no reasonable man could be expected to foresee it." This test gives prosecutors a wide scope to argue that the victim’s panicked reaction was foreseeable.
A stricter and more absolute principle is the ‘thin skull’ rule, which dictates that the defendant must ‘take their victim as they find them’. This means that if the victim has a pre-existing vulnerability—be it physical, mental, or religious—that makes them more susceptible to harm, the defendant is fully liable for the consequences. The leading case is R v Blaue [1975] 1 WLR 1411. The victim, a Jehovah’s Witness, was stabbed by the defendant. She required a blood transfusion to save her life but refused it on religious grounds and subsequently died. The defendant argued that her refusal was unreasonable and broke the chain of causation. The Court of Appeal dismissed this argument, with Lawton LJ stating that "it has long been the policy of the law that those who use violence on other people must take their victims as they find them." This rule applies to the "whole man, not just the physical man," including their beliefs. The rule is not based on foreseeability but on a clear policy that a defendant cannot use the victim’s unique characteristics as a defence.
Conclusion
The law on causation in England and Wales has developed a framework that begins with the simple ‘but for’ test and moves to the more complex, value-laden assessment of legal causation. The principles surrounding a novus actus interveniens demonstrate the law's underlying policy objective: to hold individuals accountable for the consequences of their unlawful and dangerous acts. This is clear from the high threshold set for an intervening act to be considered sufficient to break the chain of causation. The decisions in cases like Pagett and Cheshire show a strong reluctance to allow the actions of third parties, particularly medical professionals performing their duty, to absolve the initial wrongdoer. Similarly, the thin skull rule in Blaue ensures that a victim’s pre-existing vulnerabilities cannot be exploited as a defence. While this approach provides a degree of certainty and ensures that culpable defendants are held to account, it can be criticised for its potential harshness, especially when a subsequent event, such as grossly negligent medical care, is a more immediate cause of death. Ultimately, the doctrine of causation is less a set of scientific rules and more a "moral reaction" (Simester and Sullivan, 2019, p. 110), where the courts' common sense and policy considerations play a decisive role in attributing criminal blame.
References
Herring, J. (2022) Criminal Law: Text, Cases, and Materials. 10th edn. Oxford University Press.
Simester, A. and Sullivan, G. (2019) Simester and Sullivan's Criminal Law: Theory and Doctrine. 7th edn. Hart Publishing.
R v Blaue [1975] 1 WLR 1411.
R v Cheshire [1991] 1 WLR 844.
R v Jordan (1956) 40 Cr App R 152.
R v Kimsey [1996] Crim LR 35.
R v Pagett (1983) 76 Cr App R 279.
R v Roberts (1971) 56 Cr App R 95.
R v Smith [1959] 2 QB 35.
R v White [1910] 2 KB 124.
R v Williams and Davis [1992] 1 WLR 380.
